In the control of fluid in industrial processes, such as oil and gas pipeline systems, chemical processes, etc., it is often necessary to reduce the pressure of a fluid. Adjustable flow restriction devices such as flow control valves and fluid regulators and other fixed fluid restriction devices such as diffusers, silencers, and other back pressure devices are utilized for this task. The purpose of the fluid control valve and/or other fluid restricting device in a given application may be to control flow rate or other process variables, but the restriction induces a pressure reduction inherently as a by-product of its flow control function.
One device currently available for reducing pressure of a fluid utilizes a tortuous fluid flow path technique. In this technique, the fluid flow is required to pass through a device having a plurality of fluid flow passages, each of which is constructed so as to require the fluid flow to change directions many times in a tortuous path as the fluid traverses from the device inlet to the device outlet. Each of the tortuous flow paths may be divided into at least two sub-flow tortuous paths. These devices are commonly known as "tortuous path trim devices".
In such currently available tortuous path trim devices utilizing a tortuous path technique, several deficiencies have been noted which significantly reduce the desired performance characteristics of these devices.
First of all, the jet flow in each tortuous flow passage obtains a significant momentum at an angled direction immediately before being required to split and change directions into an additional two sub-flow tortuous paths or passages. This leads to an unbalanced mass flow between the two sub-flow paths, in that the sub-flow path more in line with the jet flow momentum immediately before flow splitting contains more flow mass than the associated sub-flow path which is not in line with the jet flow momentum immediately prior to the jet flow entering the split sub-flow passages. Such an unbalanced mass jet flow creates more noise and reduces the effectiveness of the tortuous path trim device.
In addition, at the outlet stage of the jet flows in each of the flow path or sub-flow paths, the inherent tortuous path trim design results in the outlet jets colliding with each other which creates additional noise in the system.
FIG. 2 illustrates a prior art disk 30 from a prior tortuous path trim device. The disk 30 includes a hollow center portion 32 and an annular perimeter 34. A plurality of tortuous flow paths are provided between the hollow center 32 and the annular perimeter 34. On the disk 30, there is formed on one disk face a plurality of flow sub-dividing and confining passageways 36 in which the fluid flow from the disk center enters the passageway 36 from the hollow center 32 and is directed through successive right angle turns--i.e., in FIG. 2, circumferential clockwise, radial, circumferential counter-clockwise, and radial directions, etc., before encountering a splitting sub-flow section 38. In each splitting sub-flow section 38 the flow is split into two sections, each of which is then required to undergo several right angle changes in direction until finally exiting as an outlet flow jet at outlet sections 40a and 40b.
In the prior art tortuous flow path disk 30 shown in FIG. 2, it can be seen that the flow jet at outlet 40a has made a right turn forward the radial heading into the outlet with the flow momentum being towards the left, whereas the flow jet at outlet 42b is making a final left turn toward the radial heading into the outlet with the flow momentum being towards the right, and this leads to the outlet jets at the adjacent, respective outlets 40a, 42b colliding and thereby increasing the noise in the system. The same collision of jets at the outlet stages occurs for instance, at the adjacent outlet stages 40b and 44a, and around the entire perimeter of the prior art disk 30, as well as between overlapping outlet stages in respective disks in a stack.
In addition, it can be seen that immediately before entering the split sub-flow section 38 in each of the passageways 36, the flow momentum is in the right circumferential direction or clockwise direction of FIG. 2 so that the momentum tends to carry more flow mass into the rightward section of the split sub-flow section 38, than in the other or left direction (counterclockwise) direction of fluid flow.
The above recited deficiencies and others in currently available tortuous path trim devices significantly reduce the effectiveness of these devices in providing desired noise attenuation. Accordingly, it is desired to eliminate the above deficiencies as well as to provide other improvements in the tortuous path trim devices so as to enable such devices to provide enhanced noise attenuation characteristics.